The study investigates the spatiotemporal evolution of multi-scale crack damage fractures in shale fracturing by employing a combination of acoustic emission and CT scanning techniques

Volume fracturing technology is a pivotal technical approach for enhancing the development of shale oil. It creates complex fracture networks influenced by factors such as the anisotropy of shale, bedding planes, and the extent of natural fractures. Despite its significance, the spatiotemporal evolution of multi-scale crack damage during shale fracturing, under varying in-situ geostress differences and construction parameters, remains unclear. To address this, this study introduces an experimental method that integrates CT scanning and acoustic emission monitoring to examine the full expansion process of fracturing. The method employs 300mm×300mm×300mm rock samples subjected to different in-situ geostress differences and construction parameters. The study clarifies the crack propagation morphology and quantity at various times and quantitatively describes the crack stimulation area before and after fracturing. The findings suggest that shale with lower minimum horizontal stress is more susceptible to crack initiation. Under high in-situ geostress differences, reservoirs with well-developed bedding planes tend to form vertical fractures, a phenomenon attributable to the stress concentration effect on these planes. An increase in injection rate from 35ml/min to 50ml/min led to a 159% increase in fracturing crack height, from 7.1cm to 18.4cm, indicating that higher injection rates promote deeper crack penetration by increasing fluid pressure and reducing stress concentration at the fracture tip. Similarly, increasing the fracturing fluid's viscosity from 2mPa·s to 50mPa·s resulted in a 52% increase in crack height, from 7.1cm to 10.8cm, highlighting the benefit of higher viscosity in reducing filtration loss and maintaining injection pressure. The combined use of high and low viscosity fracturing fluids (5:5 ratio) leverages the advantages of both approaches: forming long and high main fractures to overcome near-wellbore bedding plane constraints and then activating additional bedding planes to enhance reservoir stimulation efficiency. This research offers a theoretical foundation for optimizing fracturing crack propagation morphology and construction parameters in shale reservoirs with significant bedding planes.